Engines may include humidity sensors for determining humidity, and mass air flow (MAF) sensors for determining a flow rate of intake air to the engine. The humidity and MAF values determined from these sensors may then be used to adjust engine operation. As one example, humidity determined from the humidity sensor may be used to adjust EGR flow to engine. Further, engines with or without EGR need an estimate of air dilution to optimally set the ignition timing, among other controls. Combustion air dilution may be determined based on humidity measurements using humidity sensors.
Further, mass air flow determined from MAF sensor may be used to estimate a cylinder air charge, which may be used to determine an amount of fuel injected into an engine cylinder for combustion during engine operation.
However, humidity and MAF sensors may degrade over time or become stuck at certain readings. As a result, engine control is degraded.
In regards to humidity sensors, one attempt to diagnose functioning of the humidity sensor in the engine intake includes comparing the output of the humidity sensor to other engine sensors positioned away from the humidity sensor. One such approach for diagnosing a humidity sensor is illustrated by Xiao et al. in U.S. Pat. No. 7,715,976. Therein, humidity sensor degradation is determined based on a comparison of an intake humidity estimated by a first humidity sensor in the intake manifold with an exhaust humidity estimated by a second humidity sensor in the exhaust manifold and an ambient humidity estimated by a third humidity sensor located outside of the engine. During conditions when all the sensor readings are expected to be substantially equal, such as during engine operating conditions in which the EGR valve is closed, if the readings of the three humidity sensors differ by more than a threshold, humidity sensor degradation may be determined. Another approach for diagnosing humidity sensor is shown by Jankovic et. al. in U.S. Pat. No. 9,382,861. Therein, humidity sensor degradation is indicated if a humidity sensor output does not correlate with an intake gas composition output. For example, if the humidity sensor detects an increase in humidity, and the intake gas compositions sensor does not detect a corresponding decrease in intake air oxygen composition, degradation of humidity sensor is indicated.
The inventors herein have identified a potential issue with such approaches for humidity sensor diagnostics. As one example, the accuracy of determining degradation of any one humidity sensor may depend on the proper functioning of the other sensors. Further, multiple humidity sensors may not be needed for engine control, and thus additional humidity sensors may not be available for comparison.
In regards to MAF sensor, one example approach for diagnosing a MAF sensor includes comparing an actual mass air flow determined based on an indication from the MAF sensor to a predicted MAF based on MAP sensor output, throttle position, and engine speed. If an error between the actual MAF and the predicted MAF is greater than a threshold, MAF sensor degradation is indicated.
However, the inventors herein have recognized potential issues with such approaches for MAF sensor diagnostics. As one example, since the diagnostics requires additional sensors, such as MAP sensor, the results depend on the proper functioning of the additional sensor. For example, drift and variability of the MAP sensor decreases the accuracy of MAF sensor diagnostics. Further, the above-mentioned process for MAF diagnostics requires that the engine be operated. Due to various engine-running noise factors, such as vibration, erratic driving conditions, hot engine temperatures, etc., diagnosing MAF during engine running conditions may further reduce the accuracy of the diagnostics. Furthermore, in vehicle systems that do not have a MAP sensor, an approach to diagnose MAF degradation is required.
In one example, the issues described above for diagnostics of intake manifold humidity and MAF sensors may be addressed by a method, comprising: during a first condition when an engine is combusting fuel, adjusting engine operation based on an output of a sensor disposed in an intake of the engine; and during a second condition when the engine is off, indicating degradation of the sensor based on an output of the sensor while flowing air from an evaporative emissions system past the sensor. In this way, degradation of sensors disposed in the engine intake may be determined without relying on additional sensors, and without the impact of engine-running noise factors.
As one example, during engine off conditions, when an engine coolant temperature stabilizes near atmospheric temperature, an evaporative level check module (ELCM) pump in an evaporative emission system of the vehicle may be operated in a pressure mode to flow ambient air from the evaporative emissions system to the intake manifold via a canister and a canister purge valve (CPV). As the intake manifold humidity sensor and the MAF sensor are disposed within the intake manifold, air is flown past the humidity and MAF sensors from the evaporative emissions system. Based on humidity (which is purposely increased during humidity sensor diagnostics as discussed below) of the air, and flow rate of the air pumped into the intake manifold, humidity, and MAF sensor degradation may be respectively diagnosed.
For example, when conditions for humidity sensor diagnosis are met (e.g., flag for humidity sensor diagnostics set and ambient humidity greater than a threshold), air pumped by the ELCM has high humidity. The humidity of the air in the evaporative emissions system may be further increased by pressurizing the air with the ELCM pump and heating the air by turning on a heating element of the canister. When pressurized and heated air is released into the intake manifold, due to the larger volume and the lower temperature of the intake manifold, the air expands and cools down. This causes water vapor in the air to condense. As a result, upon opening the CPV, humidity of the air in the intake manifold suddenly increases. If the intake manifold humidity sensor is functional, the humidity sensor output may indicate an expected increase in intake manifold humidity. If the intake manifold humidity sensor is degraded or stuck, the increase in intake manifold humidity may not be sensed by the humidity sensor, and accordingly, degradation of the humidity sensor may be indicated. In this way, by generating water vapor onboard by utilizing the ELCM pump during engine off conditions, intake manifold humidity sensor diagnostics may be performed without the use of additional sensors and without the influence of engine running noise factors.
In another example, when conditions for MAF sensor diagnostics are satisfied (e.g., flag for MAF diagnostics set), a throttle valve may be opened, and intake valves of all the cylinders may be adjusted to a closed position (no valve lift) so as to direct air flow from the evaporative emissions system into the intake manifold. After the CPV is opened, the MAF sensor may be monitored for an output that is equivalent to the calibrated flow rate of the ELCM pump. If the flow rate based on the MAF sensor output is within a threshold error limit of the ELCM flow rate, MAF sensor functionality may be confirmed. If the flow rate based on the MAF sensor output is outside the threshold error limit, MAF sensor degradation may be indicated. In this way, during engine off conditions, the MAF sensor is rationalized by reverse flow (that is, flow in a direction opposite to air flow in the intake manifold during engine operation) at a calibrated flow rate by utilizing the ELCM, thereby reducing the need for additional sensors, and reducing the influence of engine-running noise factors.
In another example, in addition to diagnostics for humidity and MAF sensors, the reverse flow generated by the ELCM may be utilized for regenerating particulate filters present in some vehicles. For example, in vehicles equipped with direct fuel injection (DI), during stratified burning operation, soot may be generated. A particulate filter may be disposed in the exhaust system to capture the soot particles. Over time, the particulate filter may become clogged with soot. Accordingly, the particulate filter may be periodically regenerated by oxidizing stored particulate matter. A regeneration reaction requires oxygen and suitable temperature conditions. One example approach for regenerating particulate filters to remove soot includes during engine combustion, commanding a lean air-fuel ratio to send excess oxygen to an electrically heated particulate to further heat the particulate filter and thereby, increase the temperature of the particulate filter. Heating the particulate filter, combined with excess oxygen, causes the soot to burn. Another example approach for generating particulate filters include spinning the engine (via a motor, for example) without combusting during deceleration fuel shut off (DFSO) in order to provide oxygen to the particulate filter. However, inventors herein have identified issues with such approaches. For example, regenerating the particulate filter by operating or spinning the engine during vehicle cold start conditions (when exhaust catalyst is below light-off temperatures) may result in increased emissions.
One example approach to address the above-mentioned issues for GPF regeneration includes during engine off conditions, utilizing the reverse flow generated by the ELCM to flow ambient air into the intake manifold, and directing the flow from the intake manifold towards the particulate filter via a cylinder (e.g. by maintaining intake and exhaust valves of the cylinder in overlapping open positions, and closing the throttle valve) in order to provide more oxygen to the particulate filter for heating and regeneration. In this way, a particulate filter may be regenerated without running or even spinning the engine. Further, by utilizing the ELCM to supply oxygen, the particulate filter may be regenerated during an electric mode of vehicle operation in hybrid vehicle systems.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.